Glow plug



Dec. 17, 1935. H. RABEzzANA GLOW PLUG Filed July 21, 1952 Patented Dec.17, i935 GLOW PLUG Hector Flint, Mich., saigner, b

mesne assignments, to General Motors Corporation, Detroit, Mich., acorporation of Delaware Application July 21, 1932, serian No. 623,710

2 claims. (c1. 12s- 145) This invention relates to ignition devices forinternal combustion engines and particularly to glow plugs for use withthe .compression ignition itype of engine.

As an aid to starting, engines are sometimes equipped with a plugextending through the combustion chamber wall and carrying a resistancewire which can be heated to incandescence by the passage therethrough.of electric current of rela- -tively low voltage. Because of the lowvoltage and the conditions to which the plug is subjected, it has beendimcult to produce a plug which will stand up and give satisfactoryservice for any appreciable length oi time. The intense heat ofcombustion and the chemical changes that take place in an enginecombustion chamber cause oxidation and corrosion of the wire whichdestroys the electrical contact between the ends of the wire and theparts to which the wire is connected. vTo avoid troubles of this sort,it is hereproposed to fasten the ends of the resistance wire at as coola spot possible and beyond the zone of greatest heat and to protect thecontact against excessive oxidation.

A construction to accomplish this purpose is illustrated in theaccompanying drawing wherein optional plug structures are shown in thescctional views, Figures 1, 2, and 3.

Referring tothe drawing, the plug shown in Figure 1 includes inner andouter metallic members I and 2, respectively, suitably insulated Afromone another. The outer member or shell 2 is here shown as provided witha hexagonal head 3 for engagement by a wrench to facilitate installationand removal of the plug, and with a dependent screw threaded skirt Iadapted for engagement with a screw threaded opening in the wall of theengine through which it is grounded. Interposed between the inner andouter members for insulation purposes is a tube 5 of mica or the likeand upper and lower bodies of mica washers E and 1. seated at oppositeends against an enlarged head 8 on the lower end of the central rod Iand against a sleeve 9 of brass, copper or other ductile metal, whilethe upper body 6 rests against the top surface of the head 3 and theundersurface of a coupling or terminal nut I threaded or otherwisefastened on the upper end of the central member and adapted forconnection with the usual ignition cable. To hold the parts in assemblyand prevent leakage therethrough, the outer shell, at the time ofassembly, may be heated at an intermediate portion and placed underaxial pressure to collapse the same and The lower mica body 1 is causean inward bulge as at II', which deforms the sleeve 9 and through thesleeve exerts an inward compression of the mica tube 5, whereby the tubetightly hugs the adjacent portion of the central rod I.

The inner and outer metallic members' I and-2 carry a suitable glow wireor resistance element at the lower end of the assembly, the intermediateportion of which is shown in the form of a helical coil I2 with one endportion' I3 turned upwardly and projected into an opening ir the bottomof the skirt, extending upwardly into the body of the shell andpreferably beyond the skirt portion engaged by the wall of thecombustion chamber. At its upper end,` as at Il, the porl5' tion I3enclosed within the skirt, is staked, welded, or otherwise secured totheshellv for the purpose of making an electrical contact therewith. Theopposite end portion I5 extendsup-l wardly through an opening in thecentral rod I and at its extremity is secured to either the member I orto the terminal connector III by silver solder, staking or the like. forcontact purposes. It will be seen, therefore, that both ends of theresistance wire'are electrically connected to their 25 respectiveconnector portions at points consider'- ably removed from the hot end ofthe plug and are saved from eiIects of the intense heat and protectedagainst oxidation.

The plug heretofore describedwill be found suitable for use with a sixvolt ignition system, but for those systems where the -voltage ishigher, for example in the neighborhood of twelve volts, the diameter ofthe resistance wire must be materially reduced and in order to giveproper support for the wire it is proposed to mount the exposed portionon the lower end of the central member as shown in Figure 2. In thisgure, the inner and outer metal parts I1 and I8 are insulated from eachother by mica or 40 an equivalent tube I9, and are held together by thethermoplastic collapse of the restricted neck 20 of the shell I8, whichdeforms a ductlle sleeve 2| to seal the parts-and transmit thedeformation pressure to the mica tube. The lower portion of the centralrod I'I, which projects beyond the-bottom of the skirt, may be providedwith a helical groove in which is seated the coil 2l of the resistancewire, one end of which projects up through the member I1 and is securedat 24 50 at the top with the other end projecting upwardly through theskirt of the outer member I8 and being secured thereto as at 25.

In this particular construction, an enamel or an oxidized coating isprovided on the'exposed 55 surface of the central rod I1 and below theinsulator tube IS, to assist in the insulation of the inner and outermetal members from each other.V

Obviously such coating insulates adjacent turns 5 of the glow wirecoiled upon the rod. It may even be found practical for some uses tocoat the entire outer surface of the central rod and entirely eliminatethe need for the separate insulator sleeve i9. m A porcelain coreinsulator is. illustrated in Figure 3 where the core is formed in twopieces 21 and 23, respectively. The outer shell 29 in this case isprovided with an internal shoulder 3l at its lower'end forming a seatfor a gasket 3| and the base of the insulator 21. It is also providedwith a flange or lip 32 which may be pressed or spun inwardly over agasket 33 seated on the upper end of the core 21. 'I'he lower insulatorsleeve 28 bears at opposite ends against thebottomofthecore21andanenlargedhead 3l at the lower end of the central rod 35, whichprojects upwardly through the core 21 and carries at its upper end acoupling nut 36. The bottom of the nut 36 is preferably provided with 25a dependent skirt 31 which encloses a sealing gasket 33 and a washer 38interposed between the nut and the core 21. The resistance coil Ill inthis case is wound about and seated on the sleeve 28 with its oppositeends extending 30 through and connected to the inner and outer membersas before described. In this connection the two part insulator isimportant because of the tremendous difference of temperature existingbetween the lower end of the plus and theupperend.Ifthecoreweretobemadein a single piece, the temperature dinerence wouldcause it to crack. However, by providing a separate insulator sleeve atthe lower end, crackling iseliminatedbecausethisbodyissubjectedto asomewhat uniform temperature throughout its mass, and furthermore, itcan be of a diiferent composition from that of the main core body, andbe selected because of its ability to withstand high temperatures. 0nthe other hand, 5 the material in the main core only needs to besuitable for taking the pressure exerted upon it between the seat 38 andpressed in flange 32.

l. A glow plug for use with compression ignim tion engines and adaptedto be secured in an aperture in the wall of the combustion chambercomprising a central member having a substan tially axially extendingbore therein of uniform diameter from end tb end, an outer shell havingl5 a skirt portion to be secured in said wall and being provided with abore of uniform diameter extending upwardly beyond the portion to bereceived in the wall, and a glow wire having a portion of its lengthintermediate its ends ex- 20 posed within the combustion chamber withthe upwardly extending ends thereof completely lilling the respectivebores before mentioned and connected with both the central member andthe shell outside the wall of the combustion 25 chamber when the plug isin operating position.

2. In a glow plug, an outer shell, an insulator core mounted in saidshell, a central spindle having its lower end projecting beyond the coreand terminating in an enlarged head, an ex- 30 posed sleeve fitted tothe projecting spindle end between said head and the bottom of the core,and composed of insulating material having heat resistance propertiesdiiferent from the material of said insulator core, and a glow wireconnec- 35 tion between the spindle and shell, having an intermediateportion coiled upon and suppOrted by said insulating sleeve.

HECTOR RABEZZANA.

